1. Field of the Invention
The present invention relates to a working vehicle with a transmission arrangement that transmits drive power from an engine to a drive axle.
2. Related Art
A vehicle such as a working vehicle is designed so as to transmit drive power from an engine to a drive axle via a speed change unit, enabling the drive axle to be rotated at a desired speed by operating the speed change unit. Where it is desired to widen a speed change range of the drive axle, and/or reduce the load applied to the speed change unit, a sub-speed change unit is provided in addition to a main-speed change unit.
FIG. 19 illustrates a model view of a conventional vehicle with the main- and sub-speed change units provided and a rear axle serving as the drive axle. As illustrated in FIG. 19, aligned in the conventional vehicle equipped with the sub-speed change unit from a first side to a second side relative to a fore and aft direction of the vehicle are engine 801, flywheel 802, main-speed change unit 803, sub-speed change unit 804 and driving axle unit 805, which are connected in tandem in such a manner as to be separable from each other. This specific arrangement may cause a problem as mentioned below.
In the conventional vehicle with the sub-speed change unit, the independent units, that is, the engine 801, the flywheel 802, the main-speed change unit 803, the sub-speed change unit 804 and the axle unit 805 respectively have housings, through which they are connected in tandem, resulting in generating substantially no space between front and rear wheels. This causes a need to mount a step bar or board for the driver's seat above either of the housings, which arrangement causes the step bar or board to be mounted at a higher position, and or all of the housings to be mounted at a higher place in case where a mid-mount mower is provided between the front and rear wheels, thus undesirably inviting a higher center of gravity.
Also, in the conventional arrangement, where an HST (Hydro-static transmission) is used as the main-speed change unit 803, the HST itself vibrates due to pulsation or the like of working fluid circulated therein. This vibration of the HST may be transmitted to vehicle frame 800 via the sub-speed change unit 804 and the axle unit 805 because the main-speed change unit 803, the sub-speed change unit 804 and the axle unit 805 are connected in tandem, as described above. As a result, the ride quality of the vehicle may be deteriorated.
To address the above problems, there has been proposed an arrangement where the engine is connected with the sub-speed change unit through a housing, and the HST serving as the main-speed change unit is connected with a front side of the sub-speed change unit via a vibration absorbing member, while a front side of the HST is connected with the housing via another vibration absorbing member. However, in this arrangement, vibration of the engine is not taken into account at all. Accordingly, there cause a problem that the housing itself, which supports the HST through the vibration absorbing arrangement, vibrates due to vibration transmitted from the engine.
According to need and/or desire, the working vehicle is equipped with a hydraulic lift unit for lifting a working implement. Hitherto, the hydraulic lift unit is mounted on an upper side of a transmission case of a transmission or inside of the transmission case. In this arrangement, load generated when the working implement is moved upward or downward is applied on the transmission case. For this reason, the transmission case must be strengthened in this conventional arrangement.
In order to address the above problems, it is an object of the present invention to provide a working vehicle with a transmission arrangement transmitting drive power from the engine to the drive axle via the main- and sub-speed change units, which is capable of widening the speed change range of the drive axle and/or reducing load of a speed change mechanism, as well as effectively limiting expansion of the vehicle's length while securing a free space between the front and rear wheels.
It is another object of the present invention to provide a working vehicle that is capable of effectively preventing transmission of vibration from the engine, the main-speed change unit or the like to the transmission, the axle or the like, thus avoiding discomfort to the driver of the vehicle.
It is still another object of the present invention to provide a working vehicle equipped with a hydraulic lift unit for moving a working implement relative to the vehicle frame, which is capable of reducing the load to the transmission case, which is generated by the movement of the working implement.
It is yet another object of the present invention to provide a working vehicle equipped with an HMT made up by the combination of a variable output HST and a planetary gear unit, which is capable of minimizing the size of the HST, and widening the running speed changing range, while easily producing freewheel state of the driving wheels.